What is Solar PV?
Unlike a solar hot water system that uses the sun’s energy to heat water, solar electric or photovoltaic technology uses the sun’s energy to make electricity. Learning from the word itself, the prefix “photo” means “produced by light,” and the suffix “voltaic” refers to “electricity produced by a chemical reaction.” PV technology produces electricity directly from the electrons freed by the interaction of sunlight with certain semiconductor materials, such as silicon, in the PV module. The electrons are collected to form a direct current (DC) of electricity.
A complete solar PV system usually consists of one or more modules connected to an inverter that changes the PV’s DC electricity to alternating current (AC) electricity to power your electrical devices and to be compatible with the electric utility grid. Batteries are sometimes included in a system to provide back-up power in case of utility power outages.
How do I know how what size system I will need?
There is no one right size for photovoltaic systems. Every site is different and the needs of system owners vary, too. System size depends on several factors, including how much electricity (in kilowatt-hours or kW-h) you consume, the orientation of the system, the tilt of the system, available space and funds.
The first step to determining the size of the photovoltaic system you’ll need is to reduce consumption. Saving electricity is typically cheaper than generating it. Also, the smaller your overall consumption, the smaller and cheaper the system you’ll need. The second rule in photovoltaic system sizing is DON’T oversize system. Utilities will not credit you for any excess electricity generated on an annual basis; in other words, in any twelve month period, if you generate more than you need, the excess electricity goes into the grid and you will receive no credit.
You should try to size your system equal to or less than your annual consumption. An easy rule of thumb is to take your annual consumption (in kWh) and divide that by 1300 kWh/yr. (1kW of photovoltaics will generate about 1300 kWh per year). This will give you an estimated system size. For example, the Smiths consume 6000 kWh per year. If we divide 6000 by 1300 we get 4.6. This means the Smiths need about 4.6 kilowatts (kW) of photovoltaics to completely offset their annual consumption.
And finally, the easiest way is to have at least three electric bills handy and call for a consultation.
What is a “net-metering grid-tie” PV system?
Today in California and many other states you may connect your solar system directly into the wires of your utility. “Net Metering Laws” allow you to do this and you will actually be spinning your meter backwards when your system is generating more power than you are consuming. Thus you can ‘sell’ electricity back to the utility, up to the amount you would have used. Without Net Metering you would be forced to ‘sell’ the energy back to the utility at a lower or wholesale rate and buy it back at a much higher retail rate. Net Metering is one of the principle reasons solar electricity has become economically viable
What is the payback?
Payback is immediate, if you were to finance your solar system your payments would typically be less than the electric bill that it replaces. A solar system will also add value to your property, reduce your monthly expenses and insulate you from higher and higher energy costs. If you were to pay cash for your system, at today’s rates, you will typically recover all your investments within the next 6-10 years, but as rates go higher the time it will take to fully recoup your investment could easily be less than 5 years.
How do I know if my site will work for a PV system?
Solar designers look for sites that provide an optimal southern orientation, good exposure to the sun, and an adequate amount of structural support and space for solar panels to be placed.
The best location for a PV system is on a south facing roof, but an east or west facing roof might also work. Flat roofs provide an environment for a variety of solar modules. Locating the PV system on the ground can work with either a fixed mount or a tracking mount system.
If the space or the solar exposure for a PV system is limited, consider going to a system with a higher efficiency rating. They are more expensive but make more energy with less square footage of module space.
Can PV systems produce power on cloudy days?
Yes. Although a PV system may receive 80-90% less sunlight on a cloudy day, the modules can still generate electricity.
Do PV systems work well in the cold?
Yes. In fact, photovoltaic systems generate more power when the temperature is lower. Because of the shorter hours of daylight and lower angles of the sun in winter, PV modules do generate less energy than in summer.
Are PV Systems Safe?
Solar panels are a quiet, non-polluting source of energy. Like all large electrical devices, PV systems generate electricity and should be treated with care and maintained with the assistance of a solar professional.
Is the “Tilt” of my solar array important?
The Earth is tiled on its axis at 23.5 degrees and regardless of where you live the difference between the sun’s peak angles in the sky from December to June is 46 degrees. Regions closet to the poles experience seasons when the sun never shines, and six months later, seasons when the sun never goes below the horizon.
The optimum elevation angle for your solar system depends on your latitude. In general the optimum tilt angle is equal to you latitude, for this will ensure the maximum amount of sunlight over the course of a year. Even better would be to manually change the elevation of your solar collectors over the course of a year to follow the sun’s elevation in the sky.
A typical roof angle is 18 to 32 degrees. As long as the collector angle (known as “tilt”) is at least 18 degrees up from horizontal, additional tilt usually has little effect on total year-round performance. An exception would be areas with very sunny winters (as in most areas of Colorado) where a higher angle, facing the collector more directly into the winter sun, can make quite a difference.
Will my system have batteries?
Usually only if the system is ‘Off-Grid’. Batteries will be essential for the storage of electricity so you can use electrical equipment when there is no sunlight. Grid Connected PV systems don’t need batteries, however, you can have batteries with a grid connected installation if you wish to have power during power cuts, you need to determine this before the installation.
What happens during a power outage?
With a grid connected solar PV system, the inverter will automatically disconnect itself from the utility grid when there is a power outage. This is to prevent back feeding the grid and putting engineers working to restore power in danger. But, if you have a grid connected PV system with battery back up it will automatically switch to backup power with little detection. Both these systems will automatically hook back up to grid once power is restored.
Does PV add to the Resale Value of my home?
PV “System Resale Value” for your home is based upon research published in the Appraisal Journal which concluded that “The increase in appraisal value for a home is about twenty (20) times the annual reduction in operating costs due to energy efficiency measures.”. To calculate System Resale Value the first year annual utility savings is multiplied by twenty (20). Source: Evidence of Rational Market Valuations for Home Energy Efficiency, Appraisal Journal, Nevin/Watson.
I have a “?” sq. ft. home. How much will a system cost?
The size of your home isn’t the issue, but rather what your average electricity bills are and how much of that average bill you would like to offset. How much you want to offset will dictate the system size and cost.
How much space will the solar electric system take up on my roof?
A good rule of thumb is to allow 100 sq. ft. per every kilowatt of electricity the system produces. A solar electric system for a typical home will require 300-500 sq. ft.
How long will my solar system last?
Most solar panels come with a 25 year power output guarantee and are expected to last at least twice that long. The power output guarantee on the solar panels is provided by the manufacturer of the panels and states that at the end of the 25th year, the solar panel will still produce a minimum of 80% of their original power output.
When is the best time to install solar?
The best time to install solar was last year and will always be last year. Solar electricity is getting more and more expensive as the rebates drop and the panel prices increase. Fortunately electricity rates are increasing at a faster rate than the price of solar!